1. Field of the Invention
This invention relates broadly to wide angle lens systems, and particularly to wide angle lens systems comprising two, identical, plano-convex optical lenses, positioned with convex surfaces facing each other, and a bi-convex optical lens having a diameter which is larger than the diameter of the preceding two lenses.
2. Description of Related Art
One of the most primitive devices for viewing the interior of a furnace is an access door. The view is very limited and plant operators' conclusions regarding the combustion process are very qualitative and subjective. As a result, the evaluation is inconsistent among operators. This inconsistency has led to the emergence of the optical viewer.
The previous optical viewers have required that one be positioned directly behind the viewer in order to view a wide angle. However, as one would step back from the viewer, the angle of view would decrease thereby reducing the effectiveness of the viewer.
The previous furnace or burner observation devices have required the use of either a camera obscura to project the image of the furnace interior onto a round glass, a passageway with or without a glass window, or a glass window alone. These devices must be permanently installed. Usually, a glass window is the observation device in a steam generator burner for viewing the burner's flames. However, when combustion problems are encountered, one cannot usually diagnose the cause of the problems by simply viewing the flames through such a narrowly-limited field of view as provided by these devices. But by strategically positioning the Wide Angle Optical Viewer inside a burner or furnace, one can see the whole interior of the burner or furnace, allowing precise diagnosis of combustion problems. Additionally, because the Wide Angle Optical Viewer may be portable, it may be used at numerous burner or furnace observation ports.
Previously, when a simple passageway has been used in observation, persons viewing the interior have been subjected to hot combustion gases which hinder direct observation. Even with the addition of a glass window in conjunction with the passageway, the viewing of the furnace interior has been substantially hampered. There has been a need to use a passageway of such a length as to place the glass viewing surface at a sufficient distance from the furnace interior to reduce the heat encountered by the observer. This distance has greatly restricted the angle of view to the interior.
Finally, use of the camera obscura presents difficulties in that it is not portable, but instead is permanently installed, thus requiring a separate unit for each observation port. In addition, the camarea obscura requires the addition of a cumbersome light-proof chamber and viewing screen, which need cooling from air and/or water. However, each Wide Angle Optical Viewer can be portable and usable in several observation ports. Also, with the Wide Angle Optical Viewer there is no need for a light-free chamber, viewing screen, or air and water cooling attachments because it affords the observer a wide angle view regardless of the viewer's distance from the wide angle lens apparatus, and its planar, heat resistant lenses protect the inner lenses (and the observer) from high temperature gradients (thermal shock) and reflect most of the radiant heat emitted from the combustion process, thereby reducing heat transmission and allowing the interior lenses to remain relatively cool. Furthermore, the observer is protected from blow-back of shattered glass should the inner lenses break.
The related art comprises:
U.S. Pat. No. 1,896,830--Scharff, which is directed to an optical system for maintaining even illumination from a distanced, moving ray transmitter.
U.S. Pat. No. 2,312,542--Goodman, which is directed to a peep-hole device for doors. A negative, double-convex lens is positioned closest to the side of the door to be viewed, and as a positive, double-convex lens of the same diameter is towards the inside of the door.
U.S. Pat. No. 2,491,758--Nichols et al., which is directed to a peep hole for doors. The eyepiece is in the form of a single convex lens, while a double concave or object lens is mounted in the front end of the cylindrical member encasing the lenses.
U.S. Pat. No. 2,603,128--Miles, which is directed to an optical system from a distortion-corrected visual field of 85.degree. or more for use in objectives and eyepieces. The system comprises three lenses, a first lens being a meniscus, and two opposing plano-convex lenses.
U.S. Pat. No. 3,439,971--van Vliet, Jr., which is directed to a wide angle viewing device comprising two subsystems each consisting of a pair of objective lenses and a field lens. The two subsystems are positioned in tandem within a rectangular housing having highly reflective inner surfaces.
U.S. Pat. No. 3,472,577--Rosin et al., which is directed to a wide angle long eye-relief eyepiece. The eyepiece lens may be a plano-convex or double convex lens with aspheric correction incorporated into the convex surfaces(s). A triple lens composed of a convex lens in surface-to surface contact with a plano-convex lens is spaced from the objective lens.
U.S. Pat. No. 3,490,421--Pincus, which is directed to an optical observation port which utilizes the principles of a camera obscura to project a relatively wide angle image of a furnace interior on ground glass. A double convex lens positioned in the wall of the furnace provides an image on a glass viewing screen. The angle of view of approximately 60.degree. is increased by pivoting the lens in a support bracket.
U.S. Pat. No. 3,514,186--Poncelet, which is directed to a wide angle optical device comprising as refracting elements a sphere together with a converging lens element arranged in extremely close proximity to the sphere and having a diameter larger than the sphere. This second, positive element can be a pair of spaced plano-convex lenses arranged symmetrically with their convex surfaces facing each other.
U.S. Pat. No. 4,251,127--Yamaguchi, which is directed to a wide angle door viewer which can be zoomed and is readily perceptible without closely approaching the eyepiece. The viewer comprises an optical lens barrel having relatively large diameter lenses in positions of reverse Galileo system and a relatively larger diameter eyepiece on which the large view is provided for direct by distanced observation.